# Measuring SG on small (3.5l / 1g) batches

I do small batch brewing (3.5l-4l) and using hydrometer is a big pain for them, as I need to take very big amount of beer out to test it. I've learned to do OG readings with refractometer, but I get very wrong results when I do FG reading (after applying refractometer formula). Refractometer is very well calibrated (checking it before every measurement), but I get results like 3.1% brix, which yields very low FG results, like 1.001. That sounds unfeasible for "normal" yeast like US-05.

Am I doing something wrong when doing refractometer measurements? Are there any "shorter" hydrometers available, that would require smaller samples?

• I think you may need to double check your math. 3.1 Brix is ~1.012. 1.001 would be ~0.3 in Brix. Feb 3, 2015 at 17:00
• I've used adjustment formula for FG from seanterrill.com/2012/01/06/refractometer-calculator, it gives 1.001 with 10.9 OG. Feb 3, 2015 at 19:45
• I see, I thought you were converting Bx. directly to SG... Never mind Feb 3, 2015 at 20:10

I find a refractometer works great for OG, and a finishing hydrometer works best for final gravity (with presence of alcohol). I typically drink the sample, as I am mostly curious as to how the flavor is shaping up, especially once FG has settled (to gauge bulk-aging or conditioning impact on flavor).

However, I have some sours that I sometimes return the sample with (since I take so many over the long aging period). In this case, I use a wine thief and I put the hydrometer in the thief. Before I take a sample, I put both in sanitizer, then carefully drain the sanitizer. Then, with the hydrometer in the thief, gently lower both into the vessel until I get enough of a sample to get a reading. Then I carefully pull out the hydrometer and gently set it aside, then return the sample to the vessel.

I know another homebrewer who constructed a container from about 3 feet of 3" diameter pvc pipe, sealed at one end and plugged on top, mounted on a stand, so he can keep his thief and hydrometer sitting in sanitizer. He just pulls the plug and empties the thief, then pulls his sample, measures it, returns the sample, then returns the thief and hydrometer to the sanitizer in the container.

Most thief's (thieves?) are plastic, so you probably don't want to leave it sitting in the sanitizer for extended periods, as the plastic will break down over time, but you probably also don't want a glass thief, as this will greatly increase the risk of breaking your hydrometer.

Good luck!

• Wine thief is a great idea, I didn't know you can measure directly in it. I'll try it out. Feb 3, 2015 at 19:49
• The only issue is if you have a really fat hydrometer and a skinny thief. Ideally, check both at a homebrew store first. Feb 3, 2015 at 19:51
• I lied, you may have one more. In a 4l batch, your vessel may be too short to get a reading from using this method. If that's the case, you can still do this, but you need a test jar, and all three items need to sanitized. You can just pull smaller amounts and drain into the test jar. Feb 3, 2015 at 19:56

I use a small hydrometer (17cm in length) and a 50ml test tube. I rarely need more than 40ml to take a reading, so four readings would require, in total, less than 5% of you wort.

• All hydrometers I've seen were ~25cm, where can I get one that is so short? Feb 4, 2015 at 7:33
• Sorry, didn't see your question earlier. I am in Australia, where some Big W discount stores sell these small hydrometers. They are packaged and distributed by Brigalow Brewing Company, Meadowbrook, Qld., Australia. Mar 4, 2015 at 1:40
• Sorry, didn't see your question earlier. I am in Australia, where some Big W discount stores sell these small hydrometers. They are packaged and distributed by Brigalow Brewing Company, Meadowbrook, Qld., Australia. Mar 4, 2015 at 1:40

From morebeer.com: "After ethanol is present a refractometer reading will be off." That is, the refractometer is calibrated to measure sugar in water, not sugar in water/alcohol - the index of refraction is bit different for alcohol.

They provide a spreadsheet to help determine the actual gravity based on original gravity and final gravity reading.

• I do use adjustment formula for alcohol using OG. I haven't measured wort correction, but I assume it's close to standard 1.04 and the results were still off when I played with it. Feb 3, 2015 at 11:18
• Yeah, spreadsheet seems to pretty sensitive, and easily goes negative, so the OG reading has to be very accurate. What are your actual readings? Are they rounded at all? You should try to estimate the next (smaller) digit on the scale to get the best estimate of the actual value - that would be the scientifically correct way to do it.
– Pepi
Feb 4, 2015 at 3:21
• Also, as Franklin pointed out, 3°Brix is about 1.012, a very believable result.
– Pepi
Feb 4, 2015 at 3:22